A number of downhole motors used in the oil or mining industries for drilling through earth formations are mud lubricated. These earth drilling motors have an outer housing, an inner tubular member concentrically disposed within the outer housing, and a plurality of bearings disposed between the outer housing and the inner tubular member to facilitate the rotation of the inner tubular member. Mud lubrication is passed through a passage in the tool firstly, to provide some lubrication for the bearings and secondly, to dissipate heat which builds up within the tool.
Each mud lubricated tool requires a flow restricter to control the rate of mud flow. This is particularly critical at pressures in excess of 500 pounds per square inch. If the flow is too great it will "wash away" portions of the tool until the tool is destroyed. Conversely, if the flow is substantially cut off the heat will not be effectively dissipated and the tool will be destroyed by the resulting heat build up.
Mechanical seals have previously been used for the flow restricter, due to their ability to function at the pressure levels required. Mechanical seals work effectively when the tool is newly constructed, however, as wear occurs in the tool these flow restricters lose their effectiveness. It is common knowledge in the art that a critical factor in having effective sealing with mechanical seals is controlling the pressure on the seal faces. When wear occurs in bearings axial movement occurs which effects the pressure on the seal faces.